Aircraft having sustaining rotors



M y 5, 3 H. F. PITCAIRN AIRCRAFT HAVING SUSTANING' ROTORS Original Filed May 9, 1931 2 Sheets-Sheet 1 INVENTOR ATTORNEYS y 1934- H. F. PITCAIRN 1,958,444

AIRCRAFT HAVING SUSTANING ROTORS Original Filed May 9, 1931 2 Sheets-Sheet 2 lNVEyOR. I

' BY ZWM n ATTORNEYS ?atented May 15, 1934 UNITED STATES PATENT OFFI iEE AIRCRAFT HAVING SUSTAININ G ROTORS Application May 9, 1931, Serial No. 536,100 Renewed July 30, 1932 8 Claims.

This invention relates to aircraft having sustaining rotors, and is particularly useful in connection with the general type of craft in which the sustaining unit or rotor includes a plurality of individually articulated blades mounted for of craft of this type at various speeds and attitudes of forward flight as well as in vertical descent.

One of the'more important objects of the invention involves generally simplifying control and making it easier for a pilot to hold the craft to a given course.

Another object which might be mentioned at this point is the simplification of the construction of certain portions of such aircraft.

A further object contemplates enhancing the aerodynamical efiiciency of the craft in general. How the foregoing objects and advantages are obtained, together with others which will occur to those skilled in the art, will be apparent from a consideration of the following description taken with the accompanying drawings which illustrate a craft of the type above referred to somewhat diagrammatically in order to facilitate an explanation of the nature of this invention.

Figure 1 is a top view of an aircraft embodying the improvements of the present invention, a somewhat diagrammatic showing of various aerofoil sections and parts being applied to this figure for the purposes of the following description; and

Figure 2 is a front view of the craft of Figure 1.

-As will be apparent from inspection of the drawings, the craft herein disclosed is similar in many respects to that of the copending application of Juan de la Cierva, Serial No. 414,901, filed December 18th, 1929, and issued Feb. 20, 1934, as Patent No. 1,948,455. On the fuselage 3, suitable propelling means such as the propeller 4 is mounted at the forward end while, toward the rear, an empennage is arranged, this latter including substantially the usual fixed and adjustable horizontal surfaces 5 and 6, respectively, as well as fixe l and controllable vertical elements 7 and 8, respectively.

The sustaining rotor for the craft is mounted above the body or fuselage 3 preferably at the apex or top of a pyramid or pylon structure composed of a plurality of upwardly converging legs 9. The rotor itself includes a number of blades or wing elements 10 which are connected to a central axis or hub mechanism indicated in general at 11. The connection between the blades and the hub preferably includes substantially horizontally disposed as well as substantially vertically disposed pivot pins 12 and 13, for each blade, in order to afford freedom for movement 30 of one blade with respect to another within and transversely of their general path of rotative travel.

As is now known in this art, these articulations are provided in order that the blades may auto- '5 matically compensate for variations in inertia, lift, and other forces to which they are subjected, particularly in forward flight.

Additionally, the rotor blades 10 may be interconnected as by means of the cables diagrammatically indicated at 14 in Figure 1, such cables being provided for the purpose of controlling at least certain relative blade movements within their general path of rotative travel, as brought out more clearly in the copending applications of Juan de la Cierva, Serial No. 145,655, filed November 1st, 1926, and Serial No. 416,356, filed- December 26th, 1929, which were issued respectively, on May 24, 1932 and Jan. 17, 1933, as patents numbered 1,859,584 and 1,894,673. In order to 89 support the blades when they are inactive or at rest droop cables 15 are extended outwardly from an upwardly projecting part or mast 16 of the rotor head and attached to the blades at points spaced substantially from the axis or hub structure (see Fig. 2).

Still further, landing gear or alighting mechanism (including supporting and bracing elements 17, 18, 19, shock absorbers 20, and wheels 21,) is disposed beneath the body of the craft and 90 interconnected with the laterally extended and supplementary fixed-wing sections 22. With respect to this particular landing gear, attention is called to the fact that various features thereof are not a part of the present invention per se, but are described and claimed in a copending application of Agnew E. Larsen, Serial No. 528,- 280, filed April 7th, 1931, issued on July 11, 1933 as Patent No. 1,917,530.

As illustrated in Figure 1, the wing sections 1 22 may be employed to support aileron or lateral control surfaces 220. Also, as indicated in Figure 2, the wing sections 22 are preferably set at a slight positive incidence with the craft in normal cruising attitude (see dotted lines 22b indicating the trailing edges), in accordance with the teaching of application of Juan de la Cierva, Serial No. 500,064, filed December 4th, 1930, which has since issued as Patent No. 1,947,901 on Feb. 20, 1934.

At their outer ends the wing sections 22 are no provided with upwardly angled or inclined tip portions 23. Such supplementary fixed-wing sections 22 and 23 are advantageously employed in an aircraft of the sustaining rotor type for various reasons more fully pointed out in the copending application, Serial No. 414,901, above referred to. In addition, various of the reasons why the combination, in an aircraft; of rotatably mounted with substantially fixed aerofoils, is advantageous need not be considered in detail herein, although it should be borne in mind, in general, that stability under various flight conditions is an important object sought, and in particular, that the up-turned tip portions of the fixed aerofoils have a special co-operation with other parts of the craft of the rotative-wing type.

In accordance with the present invention the up-turned tip portions comprise substantially symmetrically cambered aerofoils. That is, each one of these tip portions is curved symmetrically at its upper and lower surfaces. This configuration is indicated diagrammatically in the section shown in Figure 1 at 24. Additionally, as will appear from inspection of both figures, the symmetrical tips 23 are set at a no-lift incidence when the craft is in substantially normal cruising attitude. Making particular reference to Figure 2, in which the craft is viewed from the front in normal cruising attitude, it will be seen that the trailing edge 25 of each up-turned tip 23 falls ona line midway of the upper and lower tip surfaces 26 and 27, respectively. A symmetrical aerofoil section arranged in this manner, of course, results in a normally no-lift setting with the craft in normal cruising attitude as shown.

Certain advantages of this configuration and disposition of fixed stub-wing tips will be apparent from a consideration of Figure 1 in which the "dot and dash lines 28-28. Assume now that the direction of forward movement of the craft is changed somewhat in order to cause relative airflow in the direction indicated by the lines 29-29.

i. e., slightly angled with respect to the normal lines 2828. Under these circumstances, each tip 23 will produce. an equal amount of drag at the opposite sides of the craft, so that in turning or flying in such manner as to cause the tips to move through the air in an angled fashion the net increase indrag of the tips is equal, as between the tips. The result is that stability is maintained.

The foregoing advantages will appear more clearly from a consideration of the diagrammatic showing of wing tips (in Fig. 1) just to the rear of those described. This diagrammatic showing illustrates wing tip portions 23a of the more usual non-symmetrically cambered section as indicated at 30. Various craft of the sustaining rotor type heretofore manufactured have been supplied with tip portions of this asymmetrically cambered character.

With such prior arrangements, when the craft is flying in such manner as to cause angular airflow over the tips 23a, the drag of the tips is irregularly changed at opposite sides. As will be apparent from inspection of the wing tips 23a and the relatively angled wind direction 3l31, the angle of incidence (with respect to a no-lift setting) is increased substantially at the tip of the left wing of the craft, while the incidence of the tip 23a of the right wing of the craft is decreased, sometimes even to a negative position. Additionally, the irregular effect of the air upon the tips 23a results in a large increase in the drag at the left side of the machine and, at the same time, a substantial reduction in drag at the opposide side. This condition, at times, tended to cause yawing or twisting of the craft in the air in a substantially horizontal plane, first toward one side, and then toward the other, resulting in oscillating or hunting of the craft with respect to the direction of flight.

On the other hand, where wing tips of symmetrical section are employed, swinging of the craft in one direction or the other with respect to the air-flow produces an equal increase in-drag at each side, thus maintaining the stability, with the result that manipulation of the controls, particularly the rudder 8, is materially simplified.

In addition to the foregoing advantages, the symmetrical wing tip section is desirable as it reduces the total drag of these elements to a minimum. Still further, the use ofsymmetrical wing tips simplifies manufacture of aircraft of the character herein disclosed for the reason that the wing tips may all be made entirely similar to each other and need not be formed differently for the right and left-hand sides.

Finally, attention is called to the fact that the increased stability resulting from fixed aerofoils constructed in accordance with the present invention enhances the maneuverability of this type of craft and considerably simplifies manipulation and control under various flight conditions.

What I claim is:-,

1. In an aircraft having a multi-bladed sustaining rotor, an aerofoil arranged at each side of the body of the craft and spaced therefrom,

said aerofoils being cambered substantially'symmetrically and being inclined upwardly and outwardly from each other.

2. In an aircraft having a multi-bladed sustaining rotor, an aerofoil arranged at each side of the body of the craft and spaced therefrom, said aerofoils being inclined upwardly and outwardly from each other'and being set at a nolift incidence with the craft in normal cruising attitude.

3. In an aircraft having a multi-bladed sustaining rotor, a substantially symmetrically cambered aerofoil arranged at each side of the body of the craft and spaced therefrom, said aerofoils being inclined upwardly and outwardly from each other andbeing set at a no-liftincidence with-the craft in normal cruising attitude. 4. In an aircraft, supporting means including 'a sustaining-bladed rotor arranged for displacement movements under the action of air and other forces in flight, and a substantially fixed aerofoil on each side of the craft at least in part extended upwardly and set at a substantiallystructures extended laterally of the craft, said structures having portions set at a positive incidence, with respect to a no-lift setting, with the craft in substantially normal cruising attitude, and said structures having other portions angled with respect to those first mentioned and Lassa-14 I set substantially at a no-litt incidence with the craft in substantially normal cruising attitude.

7. In an aircraft having a rotatable sustaining unit, substantially fixed supplemental-win structures extended laterally of the craft, said structures having their outer end portions inclined upwardly and outwardly and set at a nolift incidence, with the craft in substantially normal cruising attitude. 

